The invention relates generally to methods and apparatus for computed tomography (CT) imaging, and more particularly to methods and apparatus for updating rendered images using CT image projection data.
In certain known CT imaging systems, an x-ray source transmits x-ray beams towards an object of interest. The x-ray beams pass through the object being imaged, such as a patient. The beams, after being attenuated by the object, impinge upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is dependent upon the attenuation of the x-ray beam by the object. Each detector element of the array produces a separate electrical signal that is a measurement of the beam attenuation at the detector location. Attenuation measurements from the detectors are acquired separately for each detector element and collectively define a projection data set or transmission profile.
The x-ray source and the detector array are rotated on a gantry within an imaging plane around the object to be imaged such that the angle at which the x-ray beam intersects the object constantly changes. A group of x-ray attenuation measurements, e.g., projection data set, from the detector array at one gantry angle is referred to as a “view.” A “scan” of the object comprises a set of views made at different gantry angles, or view angles, during one revolution of the x-ray source and detector. The projection data sets are processed to construct images that correspond to two-dimensional slices taken through the object at various angles. One exemplary method for forming an image from a projection data set is referred to as filtered back projection technique.
Conventional CT medical imaging systems that acquire images without using a contrast agent result in poor visualization of the blood vessels of interest. Previous image-based methods utilized an entire set of views to be processed to generate an image. The use of an intravenous (IV) contrast medium enhances the images and allows a patient's anatomy (e.g., vessels) to be displayed more clearly. Using current medical imaging systems, it is often difficult to determine when the contrast medium arrives at an area of interest. Therefore, the imaging system may be turned on, and scanning of the area of interest may begin before the contrast medium arrives. At times, a non-contrast scan may be taken to establish a baseline image for the area to be monitored before delivery of the contrast medium. The baseline image may be then used to align the patient and the region of interest within the imaging device. By starting the imaging system in advance of the arrival of the contrast medium, the patient may be exposed to unnecessary radiation for a period of time. For instance, in an arterial study, the patient may be exposed to about 15 seconds of additional radiation before the contrast medium arrives at the region of interest. Furthermore, the longer the scanning period, the more intravenous contrast is administered to the patient, which increases costs and increases the risk of extravasation.
It is desirable to provide a CT system that shortens the scan times, reduces the total amount of IV contrast administered, and improves patient safety. It is also desirable to provide a CT system that can detect and monitor the flow of the contrast through region of interest with higher temporal resolution, such that early detection of the contrast in a region of interest is provided and the flow velocity of the contrast through the vein may be measured.